Color image scanners for reading or scanning color manuscripts into the data base of a host computer are becoming widely used. Color image scanners operate by scanning a color manuscript, resolving or separating the signals from the scanned manuscript into the primary colors and outputting a digitalized image signal to the computer.
A manuscript to be scanned may be thought of as being broken up into a rectangular grid of horizontal lines or rows and vertical columns, filling the area to be scanned The rectangular grid forms a plurality of elemental areas, elemental images, portions or pixels on the manuscript.
FIG. 1B is a representation of an image sensor 9 used to scan or read the lines or rows of elemental areas elemental images or pixels of a color manuscript. The image sensor 9 has three lines or rows of reading sensors in the form of charge-coupled-devices (CCDs) (not shown), with each line having a CCD for each elemental area or pixel. Each CCD in a line of CCDs delivers an image signal corresponding to the levels of brightness of the pixels read by the CCD. Each line of CCDs responds to different colors in the pixel and delivers image signals in terms of the level of brightness of a particular color contained in the pixels Each line of CCDs reads or scans the line of pixels and delivers image signals in terms of the level of brightness of the green, blue or red colors contained in the line of pixels read by a line of CCDs. As depicted in FIG. 1B, the three lines of CCDs are identified as G, B, and R, respectively. The G line of CCDs delivers image signals representing the level of brightness of the color green. The B line of CCDs delivers image signals representing the level of brightness of the color blue. The R line of CCDs delivers image signals representing the brightness of the color red.
In scanning a color manuscript, the optical box 5 (FIG. 1A) with the image sensor 9 therein, is moved relative to the manuscript 2 in the direction of the Y' arrow. As the optical box 5 is moved in the Y' direction, the three lines of CCDs sweep the manuscript 2. The direction of the Y arrow is called the subsidiary sweep directions The CCDs in each line sweep, scan, or read the manuscript sequentially in the direction of the X arrow. The direction of the X arrow is called the main sweep direction. Each CCD delivers an image signal representing the level of brightness of a primary color contained in the pixel read by the CCD.
As shown in FIG. 1B, the three lines of CCDs are displaced from each other in the direction of the Y arrow or subsidiary sweep direction. Accordingly, in using the image sensor 9 to scan a color manuscript, each line of CCDs will read different lines of pixels on the manuscript at the same time. The CCDs in each line deliver the image signals sequentially, sweeping across a line of pixels in the X direction. While sweeping in the X direction, three CCDs in the same column deliver image signals concurrently. Specifically, at the time a CCD in the G line delivers an image signal representing the brightness of the primary color green in the pixel on the manuscript read by the CCD, another CCD in the B line, located in the same column as the CCD in the G line, delivers an image signal representing the brightness of the primary color blue in the pixel on the manuscript read by the CCD in the B line. In addition, the CCD in the R line, located in the same column as the CCD in the G line and the CCD in the B line, delivers an image signal at the same time as the other two image signals, representing the brightness of the primary color red in the pixel on the manuscript read by the CCD in the R line. The scan or sweep process is repeated line by line, top to bottom, until the complete manuscript is scanned.
Since the three CCDs, as discussed above, are displaced from one another and hence, deliver image signals from different pixels on the manuscript, simply combining the three image signals would not provide a meaningful three-color image signal. However, a meaningful three-color image signal can be provided by collecting the image signals delivered by respective CCDs taken consecutively of the same pixel.
For instance, assume that the displacement between the lines of CCDs is equal to 10 lines of horizontal sweep. Then, when the CCDs in the G line are scanning a line of pixels, the CCDs in the B line are scanning a line of pixels 10 lines above the line of pixels being scanned by the G line of CCDs.
For the sake of this example, assume that the G line of CCDs is scanning the 60th line of the manuscript. Then, the B line of CCDs is scanning the 50th line and the R line of CCDs is scanning the 40th line of the manuscript, simultaneously with the G line of CCDs.
In order to provide a meaningful three-color image signal that includes image signals from the same pixel, the following steps are taken:
(1) The image signals delivered by the G line of CCDs scanning the 60th line are sequentially stored in a memory device. PA1 (2) As the image sensor 9 moves in the Y' direction (FIG. 1A), the image signals delivered by the B line of CCDs scanning the 60th line are also sequentially stored in a memory device. PA1 (3) As the image sensor 9 moves further in the Y' direction, image signals are sequentially delivered by the R line of CCDs scanning the 60th line. PA1 (4) As the image signals are sequentially delivered by the R line of CCDs scanning the 60th line, the G and B image signals for the 60th line, stored in the respective memory devices, are sequentially read out from the memory devices. PA1 (5) The image signals read out from the memory devices are collected with the corresponding image signals being delivered by the R line of CCDs scanning the 60th line to compose a three-color image signal for each pixel on the 60th line of the color manuscript. PA1 means for detecting the presence of correction objective pixels in a color image signal, PA1 means for calculating a correct brightness level for each detected correction objective pixel, and PA1 means for outputting a corrected color image signal by replacing the levels of brightness of the detected correction objective pixels in the color image signal with calculated corrected levels of brightness. PA1 an array of registers for sequentially receiving and storing discrete brightness levels of a color image signal, PA1 a plurality of detectors for sequentially examining the level of brightness of each discrete level of brightness in a non-standard signal and for concurrently examining the brightness levels of the brightness levels adjacent the distinct brightness level being examined, PA1 a comparator for comparing the results obtained by the detectors and judging whether each discrete-examined brightness level represents a correction objective pixel, PA1 a first calculator for calculating a parameter representative of the brightness level of the standard color signal, PA1 a further calculator for each non-standard color signal, responsive to the detectors and the first calculator, for calculating a correct level of brightness for each level of brightness detected as representing a correction objective pixel, PA1 a multiplexer, responsive to the comparator, for selecting either a corrected non-standard color brightness level or the discrete examined level of brightness, and PA1 an output for outputting the brightness levels of a non-standard color signal selected by said selecting means and the corresponding brightness levels of the standard color signal. PA1 detecting the presence of correction objective pixels in a color image signal, PA1 calculating a correct brightness level for each detected correction objective pixel, and PA1 outputting a corrected color image signal by replacing the levels of brightness of the detected correction objective pixels in the color image signal with calculated corrected levels of brightness. PA1 sequentially receiving and storing discrete brightness levels of a color image signal, said signal including a standard color signal and at least one non-standard color signal, PA1 examining each discrete brightness level of the non-standard color signal, PA1 determining whether an examined brightness level requires correction, PA1 calculating a correct brightness level for each brightness level determined to need correction, by using the levels of brightness on either side of the level of brightness being examined and the levels of brightness of the standard color signal, corresponding to the levels of brightness on either side of the non-standard color signal being examined, PA1 correcting the discrete brightness level determined to need correction, PA1 selecting either the corrected brightness levels or the examined level of brightness, and PA1 outputting the brightness levels of a non-standard color signal selected by said selecting means and the corresponding brightness levels of the standard color signal.
This method of obtaining a three-color image signal of a pixel that includes image signals delivered by different CCDs reading the same pixel at different times is called the correction for the "displacement" of CCDs. Correction for the displacement of CCDs to provide a three-color image signal is a relatively straight forward matter since the displacement between each row of CCDs is known as equal to 10 lines of horizontal sweep.
The invention described herein is directed at another correction. This invention is directed to correcting the problem caused when CCDs, reading the same pixel, are not in the same reading position relative to each other. Sometimes a CCD fails to be in the correct position relative to a pixel at the time the CCD reads the level of brightness of a primary color of the pixels The level of brightness read from the same pixel by the respective G, B, and R CCDs is supposed to be almost the same. The brightness level of a pixel is not dependent on color. Rather, the level of brightness read by a CCD is dependent on the level of brightness of the color of the pixel being read. Hence, if the CCDs are positioned differently relative to each other in reading a pixel, the CCDs may deliver image signals with different levels of brightness, since the CCDs are in effect reading different pixels. The problem is that an improperly-positioned CCD may deliver an image signal that misrepresents the level of brightness of a primary color in the pixel being read. When the three image signals are collected to form a three-color image signal of the pixel, the resulting three-color-image signal may also be inaccurate. This problem is referred to as the "disagreement of images." As will be described hereafter, the problem caused by the disagreement of images is more pronounced when the pixel exists at the edge portion of an image.
The movement of a CCD from the correct reading position can arise for a variety of reasons. One source of movement can be vibration, wherein the image sensor 9 is caused to vibrate. Another source of movement could be a shock induced movement of an image sensor. Spurious or unwanted movements of an image sensor can result in a disagreement of images in either the main sweep direction or the subsidiary sweep direction, or in both directions.
The effect of vibrating an image sensor may cause the CCDs to move from their proper position relative to the line, row of elemental images, or pixels being read. An example of what may take place will now be described in terms of a pixel in the 60th line of the manuscript being scanned.
First, assume a CCD in the G line of CCDs has been vibrated in the X or main sweep direction and as a result, is displaced 0.1 pixels to the right from the correct reading position relative to the read pixel Next, assume that the B line of CCDs has been vibrated, also in the X direction, at the time a B line CCD reads the same pixel in the 60th line and as a result, is displaced 0.2 pixels to the left. The effect of such movements in the X direction results in a disagreement of 0.3 pixels between the pixel reading by the G line CCD and the reading by the B line CCD. As described hereafter, with reference to FIG. 3B, such a disagreement of pixels or images will result in image signals being delivered by the G line CCD and the B line CCD having different levels of brightness for the same pixels.
As for the movement of the image sensor 9 in the Y or subsidiary sweep direction, assume a CCD in the G line of CCDs has been vibrated in the Y or subsidiary sweep direction and as a result, been displaced +0.1 lines in the subsidiary sweep direction from the correct reading position relative to the pixel. Next, assume that the B line of CCDs has been vibrated, also in the Y direction, at the time a B line CCD is reading the same elemental image in the 60th line and as a result, been displaced -0.2 lines in the subsidiary sweep direction. The effect of such movements in the Y direction results in a disagreement of 0.3 lines between the pixel read by the G line CCD and the same pixel read by the B line CCD.
The disagreement of images causes more of a problem when the elemental image being read exists at the edge portion, where the level of brightness changes abruptly. Such portions are usually the edge portion of a letter, the image of a letter, or the image of a mark. On the other hand, the disagreement of images causes less of a problem where the image is an image in which the brightness level changes slowly.
In order to illustrate the effect on image signals delivered by an image sensor that has vibrated, in the main sweep direction, in reading pixels that exist at an edge portion, reference is made to FIG. 3A and FIG. 3B.
FIG. 3A and FIG. 3B depict a small portion of manuscript in the form of several pixels of a letter image. One of the pixels exists at the edge portion of the letter image. Several other pixels, adjacent the pixel that exists at the edge portion of the letter, are also shown. FIG. 3A and FIG. 3B show the brightness levels of the pixels obtained with the letter image perpendicular to the main sweep direction. Two levels of brightness are shown: one delivered by a R (red) reading sensor and another delivered by a G (green) reading sensor.
In particular, FIG. 3A depicts the instance where the R and G reading sensors are positioned in the same reading position relative to the pixels. There is no disagreement of images in the FIG. 3A depiction. Hence, both brightness levels delivered by the R and G reading sensors are almost the same.
On the other hand, FIG. 3B depicts the instance where the R and G reading sensors are moved relative to each other in the main sweep direction in reading the same pixels. FIG. 3B represents the disagreement of images situation. In this situation, the brightness levels delivered from the pixels are different, especially from the pixel that exists at the edge portion, where the red and green brightness levels are largely different. Both brightness levels in the R image and in the G image are largely different at the edge portions resulting in a color displacement at the edge portion. Color displacement means a disagreement of images in different colors.
The method described above to correct the displacement of the CCDs cannot be used to correct the problem caused by the displacement of images.
Also, the countermeasure which gives gray balance to the edge portion is unsuitable to correct the problem caused by the disagreement of images since gray balance cannot be used for a color image.
Moreover, corrections for the problem caused by the disagreement of images is not easy since the disagreement is caused by unpredictable or indefinite events such as vibration or shock.
Thus, there is a need for providing an apparatus and method for correcting an image signal that includes variations in the levels of brightness of the colors of a pixel or image due to the movement of the image sensor from a correct image reading position. The color image processing apparatus and method, as described hereinafter, solves the problem caused by the disagreement of images in a relatively simple manner.